This invention relates to an oscillator circuit comprising a differential amplifier having a negative feedback input, a positive feedback input and an output, a first feedback network connected between the output and one of the inputs, which network determines the frequency of the generated oscillation, a second feedback network connected between the output and the other input, and a limiter element forming part of one of the feedback networks.
An oscillator circuit of this type is known from French Patent Specification No. 2,044,275. For generating an oscillation at a constant amplitude a part of the voltage at the output of the differential amplifier in this known circuit is fed back to the non-inverting (the positive feedback) input of the amplifier. The frequency-determining network is a rejection circuit which forms part of a feedback network connected to the inverting (the negative feedback) input of the differential amplifier. At the resonant frequency of the rejection circuit the negative feedback is at a minimum, thus oscillation is produced.
In this circuit the positively fed-back voltage is limited by means of Zener diodes. The voltages across these diodes must be equal and must remain equal in spite of possible variations which may be caused by tolerances, ageing, temperature fluctuations, etc. Moreover, these voltages and not easily controllable.